The present invention relates to microform viewers and more particularly concerns an improved image projector that facilitates maintenance of film path, and which, in another aspect, readily lends itself to a compact collapsible packaging arrangement of the viewer.
In typical microform viewers selected ones of a number of images formed on a film or microform are projected for enlarged display on the viewer screen. The film is positioned between a light source and projection lens system that projects light to be reflected by one or more mirrors to the viewing screen. To select an image, the film is moved in different directions through a film path which closely confines a chosen portion of the film between a pair of transparent glass flats. A major problem encountered in the use of such viewers is lack of cleanliness of the flats. The flats are exceedingly difficult to clean and maintain in a state of cleanliness because they are so close to each other. In my copending application for Microform Viewer, Ser. No. 066,935 filed Aug. 16, 1979, now U.S. Pat. No. 4,327,974, I have shown a pair of flats that are removable as a unit and, being hingedly connected to each other, can be readily moved apart for cleaning. Nevertheless, relatively complex mechanism and springs are required to removably mount these flats and care must be exercised in the direct handling of the flats themselves for cleaning, removal and insertion.
Accordingly, it is an object of the present invention to provide a projection system which further facilitates maintenance of film positioning structure.
Partly because of the small size of the images to be viewed in the microform viewer, a relatively long optical path is employed to obtain required magnification. Even with optimum bending or folding of the optical path, required viewer size is inherently incompatible with optimum compactness desired for ready handling and portability. To this end, collapsible viewers have been devised. Various types of folding and expandable mirror and screen arrangements have been provided. Film and lens systems have been shifted to extend the optical path for viewing at proper magnification. Typical of such arrangements is the viewer shown in the patent to Edelstein, U.S. Pat. No. 3,899,246, in which a pair of mirror sections, folded together to form sides of the viewer case, are pivoted outwardly to provide an elongated optical path. A folding mirror arrangement is also shown in my co-pending patent application identified above. In the Edelstein patent, the degree of magnification may be changed by moving the entire film and lens section toward and away from the reflectors and, moreover, this section may be entirely detached for projection on a fully displaced and more remote screen. Nevertheless, in the manipulation of these devices, the several moving parts must be separately moved between open and closed positions, requiring several different and independent operations. Yet proper location of all the parts in their desired positions and inadvertent detachment are not adequately assured.
Accordingly, it is another object of this invention to provide a compact collapsible viewer in which a viewing screen is automatically and positively driven between closed and display positions as a projecting section is moved between a collapsed position telescoped within the viewer case and an extended position in which it is withdrawn from its telescoping position. Another object is to provide viewer sections that are readily separable intentionally but not inadvertently.